The load index of a tire is a parameter well known to those skilled in the art that quantifies the maximum load that the tire is able to bear when mounted on a rim and inflated to service pressure. A load index of 100 corresponds to a maximum load of 800 kg.
Most passenger vehicle tires comprise:                two beads designed to come into contact with a rim, each bead comprising at least one annular reinforcing structure;        two sidewalls extending the beads radially outwards, the two sidewalls meeting in a crown comprising a crown reinforcement surmounted by a tread;        at least one carcass reinforcement extending from the beads through the sidewalls as far as the crown, the carcass reinforcement comprising a plurality of carcass reinforcing elements and being anchored in the two beads by a turn-up around the annular reinforcing structure so as to form, within each bead, a main portion and a wrapped-around portion;        an apex situated radially on the outside of the annular reinforcing structure and at least partially between the main portion and the wrapped-around portion of the carcass reinforcement, and        an outer strip positioned axially on the outside of the carcass reinforcement and of the apex.        
Recently, there have been proposals to improve the rolling resistance of passenger vehicle tires by optimizing the beads thereof. Document WO 2010/072736 notably teaches the use of special rubber compositions: the outer strip and possibly the apex are made using rubber compositions that have an elastic modulus G′ less than or equal to 15 MPa and a viscous modulus G″ such that:G″[MPa]≦0.2·G′[MPa]−0.2 MPa,the elastic and viscous moduli being measured at 23° C.
That document also recommends further reducing the rolling resistance by optimizing the geometry of those portions of the tire that have these moduli: the portion of rubber composition having an elastic modulus G′ less than or equal to 15 MPa and a viscous modulus G″ such that:G″[MPa]≦0.2·G′[MPa]−0.2 MPa,has, in any radial cross section, a thickness Ep(r), this thickness corresponding to the length of the intersection of the direction perpendicular to the main portion of the carcass reinforcement with the said portion of rubber composition, r denoting the distance separating the intersection of the said direction perpendicular to the main portion of the carcass reinforcement with the main portion of the carcass reinforcement from the radially innermost point of the annular reinforcing structure. The thickness Ep(r) changes in such a way that, in the range of distances r comprised between 20 and 50 mm, the variation in thickness
      ∂          Ep      ⁡              (        r        )                  ∂    r  is negative and has an absolute value that is greater than or equal to 0.25 mm/mm (i.e. the value is below −0.25 mm/mm) over at least 5 mm. In other words, it is advantageous to ensure that the entity formed by the apex and the outer strip is “squat”, that is say shorter and wider than in conventional tires.
When implementing this teaching in tires designed to be fitted to vehicles of the “4×4” type that have a load index in excess of 100—tires which traditionally have had very stiff (in excess of 50 MPa) apexes—it has been found that the incorporation of thick outer strips presents a problem of industrial robustness. More specifically, because the quantities of rubber composition involved are fairly great, it is difficult to prevent rubber from moving while the tires are being cured. As a result, the proportion of tires that fail to meet the specifications increases significantly.
In order to limit this problem, the applicant has found that it is advantageous to give the annular reinforcing structure a maximum axial width DE such that the ratio
                              Ep          ⁡                      (            r            )                          max            -      DE                      Ep        ⁡                  (          r          )                    max        ,where Ep(r)max is the maximum value of the thickness Ep(r), is less than or equal to 10%.
One difficulty associated with implementing these solutions is their relatively high cost which is notably due to the use of apexes and thick outer strips made of rubber compositions that have a low elastic modulus.